Exposure apparatuses for semiconductor processing are commonly used to transfer images from a reticle onto a semiconductor wafer. Typically, the exposure apparatus utilizes one or more movers to precisely position a wafer stage holding the semiconductor wafer and a reticle stage retaining the reticle. Additionally, the exposure apparatus can include a vibration isolation system that includes one or more movers. The images transferred onto the wafer from the reticle are extremely small. Accordingly, the precise positioning of the wafer and the reticle is critical to the manufacturing of the wafer. In order to obtain precise relative alignment, the position of the reticle and the wafer are constantly monitored by a measurement system. Subsequently, with the information from the measurement system, the reticle and/or wafer are moved by the one or more movers to obtain relative alignment.
One type of mover is a linear motor that includes a pair of spaced apart magnet arrays that generate a magnetic field and a conductor array positioned between the magnet arrays. Electrical current is directed to the conductor array. This causes the conductor array to move relative to the magnet arrays.
Unfortunately, the electrical current supplied to the conductor array also generates heat, due to resistance in the conductor array. Most linear movers are not actively cooled. Thus, the heat from the conductor array is subsequently transferred to the surrounding environment, including the air surrounding the linear motor and the other components positioned near the linear motor. The heat changes the index of refraction of the surrounding air. This reduces the accuracy of the measurement system and degrades machine positioning accuracy. Further, the heat causes expansion of the other components of the machine. This further degrades the accuracy of the machine. Moreover, the resistance of the conductor array increases as temperature increases. This exacerbates the heating problem and reduces the performance and life of the linear motor.